At present, biofuel production including industrial chemicals from agricultural lignocellulosic biomass has come to attentions because it's possibility in both technical and economic aspects. Basically, all agricultural lignocellulosic biomass including hardwood, softwood, and agricultural waste have lignocellulosic chemical structure which contains three main components which are: (1) cellulose which is linear polymer of glucose sugar connected to each other by 1,4-β-glycosidic bond and arranging in orderly fiber with high crystallization; (2) hemicellulose which is amorphous branched polymer composed mainly of pentose sugar such as xylose and arabinose and hexose sugar such as glucose, mannose, and galactose, including sugar derivatives, hemicellulose acting as a matrix in plant cell wall; and (3) lignin which is polymer of phenolic compounds arranging in three dimensional structure to provide strength to plant cell wall, including other minor components such as proteins, lipids, and minerals. Lignocellulosic structure is strong and durable to the physical, chemical, and biological degradations.
A sugar platform bio refinery process is a fuel and chemical production process with a high economic potential and environmental friendly. In this process, lignocellulosic biomass is digested into sugars with acids or enzymes. Obtained sugar is transformed into biofuel and other chemical products via fermentation or chemical catalytic processes. A pretreatment of agricultural lignocellulosic biomass is an important step for enhancing enzymatic digestibility of lignocellulosic biomass. Said pretreatment has direct effect on structure and chemical composition of lignocellulosic biomass which includes removing of hemicellulose, dissolving and extracting lignin, reducing polymer size of carbohydrate, and reducing crystallization of cellulose. These can result in accessibility of enzymes to cellulosic fiber, then yielding more sugar from enzymatic digestion. The pretreatment of lignocellulosic biomass can be done by chemical, thermal, and biological methods, each one has its technical and economic advantage and disadvantage and suitable for different physical structure and chemical basic character of lignocellulosic biomass.
The pretreatment of lignocellulosic biomass with organic solvent (Organosolv) is the effective process and can be applied to variety of lignocellulosic biomass in hardwood, softwood, and agricultural waste. Organic solvent can be selected from physical and chemical properties such as boiling point, polarity, including extraction specificity to lignin and hemicellulose. Ethanol and methanol are basic organic solvents in the pretreatment process of lignocellulosic biomass, whereas there have been studies on other organic solvents such as organic alkali, ketone, ester, 1,4-butanediol, butanol, and ethanolamine, including high boiling point organic solvent such as glycerol, ethylene, propylene glycol. Moreover, organic acids have been used such as formic acid, acetic acid, and peroxyformic acid. Most of the pretreatment processes using organic solvents have high selectivity which would not destroy cellulose and provide high quality and purity lignin which can be value added. Moreover, use of organic solvent reduces viscosity in the system and reduces re-precipitation of lignin on the surface of lignocellulosic biomass which is the current limitation of other pretreatment processes for lignocellulosic biomass.
The adding of catalyst is another study to increase effectiveness in pretreatment of lignocellulosic biomass using several thermochemical techniques such as high pressure steam, steam explosion, and high pressure hot water with several acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, including organic acid such as oxalic acid for the increasing of efficiency and selectivity which lead to the reduction of temperature and energy consume in the pretreatment process. While the use of alkali such as sodium hydroxide, ammonia, and limestone provides high effectiveness for increasing of sugar yield from digestion of lignocellulosic biomass. The use of alkali as a catalyst results in lignin extraction including partial digestion of hemicellulose and gives expansion to cellulose.
The pretreatment process of lignocellulosic biomass using organic solvent under alkaline condition was disclosed in U.S. Pat. No. 8,460,898B2, which included the further adding of ammonia and pretreating at a temperature ranging of 100 to 220° C. to solubilize lignin in suspension then separating desired polysaccharide. Moreover, U.S. Pat. No. 8,278,070B2 disclosed the adding of organo-mercaptan in organic solvent under alkaline condition for the increasing the effectiveness of lignin extraction.
Patent publication no. WO 2013/151927 disclosed the pretreatment process of lignocellulosic biomass using a mixture of organic solvent, alkali, and oxidizing agent. This process increased effectiveness in the separation of polysaccharide from lignocellulosic biomass. However, the pretreatment process of lignocellulosic biomass using oxidizing agent gave unwanted by-product and effected to following steps of fermentation and sugar separation.
Therefore, the pretreatment process of lignocellulosic biomass has been further developed under low temperature condition or mild condition for the specificity of removing of lignin but not destroying cellulose, including the reduction of by-product which effects the further steps in sugar production.